Jet combustion fuel



United States Patent 3,150,971 JET CGMBUSTIQN FUEL Frank G. Ciapetta, Upper Darby, Pa, and Harry L.

Coonradt, Woodbury, and William E. Garwood, Haddonfield, N.J., assignors to Socony Mobil Oil Company, Inc., a corporation of New York Filed Get. 20, 1955, Ser. No. 541,734 3 Claims. (Ci. 208-45) This invention is directed to novel fuels utilizable in jet combustion devices. It is more particularly concerned with jet combustion fuels having a combination of improved characteristics.

As is well known to those familiar with the art, the term jet combustion refers to a method of combustion wherein fuel is continuously introduced into and continuously burned in a confined space, for the purpose of deriving power directly from the hot products of combustion. The most complicated forms of jet engines presently proposed consist of a propulsion or jet tube, closed at one end, plus a gas turbine which extracts sufficient energy from the departing gases to drive the compressor. In present commercial forms, the compressor and turbine are assembled axially upon a common shaft, spaced far enough apart to permit a number of combustion chambers to be arranged about the shaft between the compressor and turbine, with an exhaust tube extending rearwardly from the turbine. The principal application of such engines is in powering aircraft, particularly for high-altitude operations. Therefore, the desiderata of fuels utilizable in jet combustion devices are many and varied.

At the present time, most jet fuels are straight-run petroleum distillates. The characteristics of such fuels, therefore, are limited by the properties of the crude source. Insofar as is now known, satisfactory jet fuels have not been made from cracked stocks. Accordingly, as the supply of jet fuels is dependent upon the availability of suitable straight-run stocks, it is sharply limited. It will be appreciated, therefore, that new sources of jet fuels are highly desirable, in view of the ever increasing demands of commercial and military consumption.

let combustion fuels, as contemplated herein, are hydrocarbon fractions that can have initial boiling points as low as about 200 F. or lower, and end-boiling points as high as about 600 F. Depending upon the particular application, a jet fuel can boil within a relatively low range of temperatures or within a relatively high range of temperatures. For example, in order to insure quick starting in the operation of military jet-propelled aircraft, jet combustion fuels that boil within rather low temperature ranges are used. These fuels, however, have a high A.P.I. Gravity, and, accordingly, they will have less weight per gallon. Indeed, the A.P.I. Gravity of presently known jet fuels increases rapidly as the boiling range of the fuel is lowered. As the weight per gallon together with the number of B.t.u. per unit weight is determinative of the amount of power per gallon of fuel, it is desirable to have the A.P.I. Gravity as low as possible. Accordingly, it would be highly desirable to have jet fuels that boil within various ranges of temperatures without substantial difference between the A.P.I. Gravity of a lowboiling-range fuel and that of a high-boiling-range fuel.

Another important characteristic of a jet fuel is the amount of the net heat of combustion, i.e., the number of B.t.u. per pound. This value is usually expressed as the product of the A.P.I. Gravity and the Aniline Number (Aniline-Gravity Product), as described in ASTM Test Methods D611 and D287. As is well known to those familiar with the art, the Aniline-Gravity Product varies directly with the number of B.t.u. per pound. Most jet fuels that have been proposed heretofore have had 3,150,071 Patented Sept. 22, 1964 Aniline-Gravity Products that are substantially lower than 6,000. In view of the foregoing, it will be seen that it is highly desirable to produce jet combustion fuels that have considerably higher Aniline-Gravity Product.

Additional important characteristics of .a jet fuel are its storage stability and its sludge-forming tendencies. These characteristics are directly related to the sulfur content, more particularly, to the mercaptan sulfur content of the fuel. The supply of jet fuels that have been derived from straight-run sources is, therefore, further limited by the fact that many crudes have relatively high sulfur contents. Indeed, resort has been had to additives to improve stability. Accordingly, it is desirable to produce, in large amounts, jet fuels that have very low sulfur and mercaptan sulfur contents.

As is well known to those familiar with the art, in the operation of jet combustion devices, deposits of a soot-like character are formed within the combustion chamber and in subsequent portions of the apparatus. These deposits cause operating difiiculties by interfering with combustion in the combustion chamber and by damaging the turbine. Soot-forming tendencies of a fuel are measured in terms of the Smoke Point, i.e., the highest flame height in millimeters at which no smoking occurs, as measured by the Institute of Petroleum Test No. 57/45. Accordingly, it is highly desirable for efficient jet engine operation that the Smoke Point be as high as possible.

Further, many jet combustion devices must be operated under low-temperature conditions, as in Arctic climates or at extremely high altitudes. Under these conditions, it is important that the jet fuel remain liquid, so that it can be transferred without the use of expensive heating devices. Accordingly, it is desirable for a jet fuel, especially the higher-boiling fuels, to have the lower possible freezing point.

The development of supersonic jet aircraft has necessitated cooling of the jet engine. This is accomplished by indirect heat exchange with the incoming jet fuel. Accordingly, the fuel is subjected to temperatures of about 400500 R, which results in the formation of gum and sediment causing plugging of filters and nozzles, and of lacquer-like deposits in the heat exchange tubes. In an attempt to alleviate this condition with conventional straight-run fuels, resort has been had to the use of additives, but inhibitor response has been poor. It is desirable, therefore, to have jet fuels available that exhibit good properties of thermal stability and which are responsive to the addition of additives.

A hydrocarbon jet combustion fuel that possesses all the aforedescribed desiderata has now been found. A jet combustion fuel boiling in the jet fuel range that is a continuously-boiling cracked distillate and has a high Aniline-Gravity Product, a low sulfur and mercaptan sulfur content, a high Smoke Point, a low freezing point, even in the higher-boiling fuel range, and no substantial variation of the A.P.I. Gravity with the boiling range has now been discovered.

Accordingly, it is an object of the present invention to provide a new, improved jet combustion fuel. Another object is to provide a new jet combustion fuel that is a continuously-boiling cracked distillate fraction. A specific object is to provide a jet combustion fuel that has all the following desiderata: a high Aniline-Gravity Product, a low sulfur and mercaptan sulfur content, a high Smoke Point, a low freezing point even in the highboiling range, and no substantial variation of the A.P.I. Gravity with the boiling range. A more specific object is to provide a jet combustion fuel that is a continuouslyboiling cracked hydrocarbon distillate fraction having all the aforementioned desiderata.

Other objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description considered in conjunction with the drawings, wherein:

FIGURE 1 presents graphically the relationship between the volume percent conversion into products boiling at temperatures varying between about 80 F. and about 330 F. and the freezing point of a typical heavy jet combustion fuel of this invention, produced by cracking light gas oil;

FIG. 2 presents graplncally the relationship between the volume percent conversion into products boiling at temperatures varying between about 80 F. and about 330 F. and the temperature to produce a typical jet combustion fuel of this invention;

FIG. 3 presents the relationship between the mid-boiling point and the Aniline-Gravity Product of the jet fuels of this invention and of typical jet fuels of the prior art;

FIG. 4 presents the relationship between the mid-boiling point and the total sulfur content of the jet fuels of this invention and of typical jet fuels of the prior art;

FIG. 5 presents the relationship between the midboiling point and the mercaptan sulfur content of the jet fuels of this invention and of typical jet fuels of the prior art;

FIG. 6 presents the relationship between the mid-boiling point and the Smoke Point of the jet fuels of this invention and of typical jet fuels of the prior art;

FIG. 7 presents the relationship between the mid-boiling point and the A.P.I. Gravity of the jet fuels of this invention and of typical jet fuels of the prior art; and

FIG. 8 presents the relationship between the mid-boiling point and the freezing point of the jet fuels of this invention and of typical jet fuels of the prior art.

Broadly, the present invention provides a cracked distillate hydrocarbon fraction that has an initial boiling point falling within the range varying between about 200 F. and about 400 F., a 50 percent-point of at least about 325 F., and an end-boiling point falling within the range varying between about 450 F. and about 600 F., and which boils substantially continuously between said initial boiling point and said end-boiling point; a boiling range of at least about 75 F.; an Aniline-Gravity Product of at least about 7,000; a total sulfur content of less than about 0.04 percent, by weight; a mercaptan sulfur content of less than about 0.0005 percent, by weight; a Smoke Point of at least about 30; a rate of change in A.P.I. Gravity of less than about 4 per 100 F. change in the 50 percent-point; and a freezing point that is lower than the value determined by the formula: 0.423(Mid-boiling Point in F.)226.

In general, the jet fuels of this invention have an initial boiling point falling within the range varying between about 200" F. and about 400 F., a 50 percentpoint of at least about 325 F., and an end-boiling point falling within the range varying between about 450 F. and about 600 F., and they boil substantially continuously between the initial boiling point and the end-boiling point. The jet fuels can be classified as lower boiling jet fuels (of the JP-4 type, as defined in Military Specification MIL-F-5624B) and as higher boiling jet fuels (of the JP-S type, also as defined in MILF-5624B). The lower boiling jet fuels of this invention have an initial boiling point falling within the range varying between about 200 F. and about 275 F. and an end-boiling point falling within the range varying between about 450 F. and about 550 F. The heavier, higher boiling jet fuels have an initial boiling point falling within the range varying between about 275 F. and about 400 F. and an end-boiling point falling within the range varying between about 500 F. and 600 F.

. In general, the jet combustion fuels of this invention can be produced by cracking gas oils in the presence of hydrogen and of a catalyst comprising one or more metals of the platinum and palladium series supported upon a synthetic composite of two or more refractory oxides. in order to produce superior jet fuels, however, the cracking charge stock used is preferably a straight-run gas oil, and the type of cracking operation selected will be somewhat dependent upon the boiling range of the charge stock. Thus, if the charge stock is a straight-run light or medium gas oil, it can be readily converted into a jet fuel of this invention in a once-through cracking operation. On the other hand, if the charge stock is a heavy gas oil, a full range gas oil, a vacuum gasoil, or a coker gas oil, the cracking operation is most feasibly carried out in a cycle operation or a multiple-pass operation.

The catalysts utilizable in the cracking operations that will produce the jet combustion fuels of this invention are those described in co-pending application Serial No. 351,151, filed on April 27, 1953; and in the continuationin-part thereof, Serial No. 418,166, filed on March 23, 1954, both now abandoned; see U.S. Patent No. 2,945,806. Briefly, these catalysts comprise between about 0.05% and about 20%, by weight, of the final catalyst, preferably between about 0.1% and about 5%, by weight, of the metals of the platinum and palladium series, i.e., those having Atomic Numbers of 44-46, inclusive, 76-78, inclusive, supported upon synthetic composites of two or more refractory oxides. The carrier is a synthetic composite of two or more oxides of the metals of Groups IIA, IIIB and IVA and B of the Periodic Arrangement of Elements [1. Chem. Ed, 16, 409 (1939)]. These synthetic composites of refractory oxides must have an Activity Index of at least about 25. They can also contain halogens and other materials which are known in the art as promoters for cracking catalysts, or small amounts of alkali metals that are added for the purpose of controlling the Activity Index of the carrier. Non-limiting examples of the composites contemplated herein include silicaalumina, silica-zirconia, silica-alumina-zirconia, aluminaboria, silica-alumina-fluorine, and the like. The preferred support is a synthetic composite of silica and alumina containing between about 1% and about by weight, of alumina. These synthetic composites of two or more refractory oxides can be made by any of the methods Well known to those skilled in the art of catalyst manufacture. Examples of methods of preparing them are set forth in co-pending applications Serial Nos. 351,151 and 418,166, both referred to hereinbefore.

The following example illustrates a method of preparing a platinum-containing catalyst utilizable in the process of preparing the jet combustion fuels of this invention:

EXAMPLE 1 A synthetic silica-alumina carrier or support containing 10% by weight of alumina was prepared by mixing an aqueous solution of sodium silicate (containing 158 g. per liter of silica) with an equal amount of an aqueous, acid solution of aluminum sulfate containing 39.4 g.

and 28.6 g. concentrated H 80 per liter. The mixture was dropped through a column of oil wherein gelation of the hydrogel was efiected in bead form. The head hydrogel was soaked in hot water (about F.) for about 3 hours. The sodium in the hydrogel was then removed by exchanging the gel with an aqueous solution of aluminum sulfate [1.5% Al (SO by weight] containing a small amount (0.2 percent by weight) of ammonium sulfate. The thus-exchanged hydrogel bead was water-washed. Then, it was dried in superheated steam (about 280-340 F.) for about 3 hours and, finally, calcined at 1300 F. under a low partial pressure of steam for about 10 hours. The silica-alumina beads were then crushed to pass through a l4-mesh screen and the material retained on a 25-mesh screen (US. Standard Screen Series) was used for catalyst preparation. 7

Catalyst A A portion of the crushed, calcined carrier was then barely covered with an aqueous solution of chloroplatinic acid, of concentration sufiicient to produce the desired amount of metal in the finished catalyst. The excess solution was removed by centrifuging. The thus-impregnated carrier was then dried at 230 F. for 24 hours. The catalyst was treated with hydrogen for four hours at 400 P. Then, it was activated in hydrogen for 16 hours before it was used. The catalyst thus-prepared contained 0.47% platinum, by weight of the catalyst, and the silicaalumina carrier had an Activity Index of 46.

Catalyst B Another portion of the crushed, calcined carrier was subjected to a vacuum of about 5 mm. Then, an amount of a chloroplatinic acid solution sufiicient to produce the final desired concentration of platinum was sorbed on the carrier. The thus-impregnated catalyst was wet-aged, i.e., aged in a covered vessel, at 230 F. for about 20 hours, and reduced with hydrogen for about 2 hours at 450 F. and for an additional 2 hours at 950 F. It was finally activated in hydrogen at about 900 F. for about 2 hours prior to use. This catalyst contained 0.5% platinum, by weight of the catalyst, and the silica-alumina carrier had an Activity Index of 46.

In general, regardless of the type of operation (oncethrough, cycle, or multiple-pass) used, the cracking process that produces the jet fuels of this invention is carried out in the presence of hydrogen in amounts, expressed as the molar ratio of hydrogen to hydrocarbon charge, varying between about 2 and about 80, preferably, between about 5 and about 50. The hydrogen pressure will vary between about 500 pounds per square inch gauge and about 2500 pounds per square inch gauge, preferably, between about 750 and about 2000 pounds per square inch gauge. The liquid hourly space velocity will vary between about 0.1 and about 5, and preferably, between about 0.1 and about 3. The cracking temperature will vary between about 500 F. and about 825 F., preferably, between about 600 F. and about 775 F.

The method of once-through cracking is fully described in the co-pending applications, Serial Nos. 351,151 and 418,166, both referred to hereinbefore. In order to produce the jet fuels contemplated herein, however, the cracking charge stock used in once-through operation is, preferably, a light or a medium petroleum gas oil, or a fraction boiling within the range of both light and medium gas oils. A light gas oil, as contemplated herein, boils between about 400 F. and about GOO-650 F. The medium gas oils between about 600-650 F. and about 700-760 F. The charge stocks, therefore, can be straight-run petroleum gas oils boiling within the range varying between about 400 F. and about 760 F. Higher-boiling gas oils, coker gas oils, etc., will not readily produce, in a once-through operation, jet fuels that have all the aforementioned desirable properties.

Excellent jet fuels can be made by the afore-described once-through operation. If it is desired, however, to produce fuels, particularly those boiling in higher temperature ranges, having a very low freezing point, it is necessary to control the cracking reaction to produce at least about 30 volume percent conversion of the charge into products that boil at temperatures Varying between about 80 F. and about 300330 F. This will be apparent from the following examples:

EXAMPLE 2 The charge stock used in this example was a straight-run Portions of the light West Texas gas oil were subjected to cracking in the presence of hydrogen and of Catalyst B described in Example 1, after the latter had reached equilibrium, i.e., had been in continuous operation for more than five days. The hydrogen pressure used was 1000 pounds per square inch gauge. The liquid hourly space velocity was 0.5 and the molar ratio of hydrogen to oil, using hydrogen recycle, was 40. Each portion of the charge stock was contacted with the catalyst under these conditions at a different temperature. A higher boiling jet fuel of the JP-S type (a higher boiling jet fuel as specified in Military Specification M]LF5624l3) was isolated from each run. Pertinent data and product properties are set forth in Table 1.

EXAMPLE 3 The charge stock used in this example was a straightrun fraction distilled from an East Texas crude. This gas oil had the following properties:

A.P.I. gravity 36.5 ASTM distillation:

I.B.P. F 456 50% F 549 E.B.P. F 684 Sulfur, weight percent 0.13

This light East Texas gas oil was cracked in the presence of hydrogen, with hydrogen recycle, and of the catalyst used in Example 2, at a temperature of about 701 F. The hydrogen to oil molar ratio employed was 40; the liquid hourly space velocity was 0.5; and the pressure was about 1000 pounds p.s.i.g. A jet fuel of the JP5 type was isolated from this run. The pertinent data and product properties are set forth in Table I.

TABLE 1 Example 2 2 2 3 Temperature, F 673 693 708 701 Cracking Level 1 25. 2 36. 4 53. l 43. 9 Heavy Jet Fuel, Vol ereenL 58. 5 65. 0 52. 3 61. 3 Jet Fuel Properties: A.P.I. Gravity 43. 9 45.0 46.6 47. 9 ASTM Distillation:

I.B.P., F 365 349 371 340 50% Point, F 434 439 435 435 E.B.P., F 543 545 537 548 Aniline-Gravity Produ 7, 165 7, 525 7, 885 8. 300 Total Sulfur, Wt. percent 0.003 0. a 0. 006 0. 002 Mereaptan Sulfur, Wt. percent. 0.0004 0.0003 0. 0003 0. 0004 moke Point 33. 3 34.0 35.1 38. 2 Freezing Point, F 48 52 61 -55 1 Volume percent conversion into products boiling between about F. and about 330 F.

The curve in FIG. 1 is based upon the data set forth in Table I. It shows graphically the relationship between the freezing point of higher boiling jet fuel (JP-5) and the volume percent conversion into products boiling at temperatures varying between about 80 F. and about 330 F. It will be noted that freezing points of 45 F. and lower are obtained even at relatively low conversion levels of about 20 volume percent. The optimum freezing point requirement of a heavy jet fuel has not been definitely fixed. At present, specifications call for 40 F., because such a freezing point represents the approximate limits of freezing point obtainable from straight-run stocks. Generally, it is believed that a freezing point of 50 F. or lower, if obtainable, would be more preferable. Accordingly, it will be noted from FIG. 1 that in order to achieve a freezing point lower than-50 F. in a heavy jet fuel, the cracking level must be controlled to obtain a conversion of at least about 30 volume percent into products boiling at temperatures varying between about 80 F. and about 330 F.

The usual temperatures at which such a conversion is effected are shown by the curve in FIG. 2, which is also based upon the data in Table I. This curve shows the relationship between the temperature and the volume percent conversion into products boiling at temperatures Varying between about 80 F. and about 330 F. It will be noted that the desired amount of conversion into jet fuels can be achieved at temperatures varying between about 670 F. and about 710 F. It will be appreciated, therefore, that the production of jet fuels in a oncethrough operation is obtained at relatively low temperatures and that the freezing point characteristics of the jet fuel are controllable through control of the conversion level.

The following examples illustrate various types of jet fuels that can be made from a variety of gas oils, in a once-through cracking operation.

EXAMPLES 4 AND 4a The charge stock used in these examples was a straightrun fraction distilled from a Kuwait crude. This material was a light gas oil having the following properties:

A.P.I. gravity 39.1 ASTM distillation:

I.B.P. F 418 50% F 506 E.B.P. F 634 Sulfur, weight percent a 0.94

This gas oil was cracked in the presence of the platinum Catalyst A described in Example 1, and in the presence of hydrogen in an amount, expressed as the molar ratio of hydrogen to hydrocarbon charge, of 40. The catalyst temperature employed was about 695 F., the liquid hourly space velocity was 0.5 and the pressure was 1000 pounds per square inch gauge. A portion of the effluent product was distilled to produce a low-boiling jet fuel, and the other portion was distilled to produce a high boiling jet fuel. Pertinent data and the properties of these jet fuels are set forth in Table II.

EXAMPLE 5 The charge stock used in this example was the same as that used in Example 3. The light East Texas gas oil was cracked in a once-through operation, in the presence of the platinum catalyst, substantially as described in Example 3 with the exception that the cracking was carried out at a temperature of about 689 F. At this temperature, 32 volume percent of the charge was converted into products boiling at temperatures of 80 to 330 F. A jet fuel fraction was obtained that boiled between about 352 F. and about 492 F. Pertinent data and the properties of this fuel are set forth in Table II.

EXAMPLE 6 The charge stock used in this run was a light gas oil obtained from. an East Texas crude. It had the following properties:

This light East Texas gas oil was subjected to oncethrough cracking in the presence of the platinum Catalyst A described in Example 1 and of hydrogen in an amount,

expressed as the molar ratio of hydrogen to hydrocarbon charge, of 40. Thecracking temperature used was about 721 F., the liquid hourly space velocity as 0.5, and the pressure was about 1000 pounds per square inch gauge. At this temperature, there was produced 73.1 volume percent, based upon the initial charge, of a light jet fuel. The properties of this fuel are set forth in Table II.

' EXAMPLE 7 The charge stock used in this run was a medium gas oil obtained from an East Texas crude. It had the following properties:

A.P.I. gravity 33.2 ASTM distillation:

I.B.P. F 418 50% F 600 E.B.P. F 760 Sulfur, weight percent 0.37

This gas oil was cracked, in a once-through operation, in the presence of the platinum Catalyst A described in Example 1 and in the presence of hydrogen to produce 68.4 volume percent of light jet fuel. The temperature used was 728 F., the hydrogen to oil molar ratio was 40, the liquid hourly space velocity was 0.5 and the pressure was about 1000 pounds per square inch gauge. Pertinent properties of the jet fuel obtained in this run are set forth in Table II.

TABLE II Example u 4 I 40 5 6 t 7 .To tFucI Yield, V01. percent M 36. 7 70. 8 66. O 73. 1 68. 4 A P.I. Gravity 49. 6 50. 6 46. 2 49. 3 4S. 5 ASTM Distillation:

I .P., I 384 220 352 230 220 50% Point, F 441 389 415 374 376 E.B.P., 522 513 492 520 540 Aniline-Gravity Pr 9, 030 8, 045 7, 555 7, 296 7, 008 Total Sulfur, Wt. pcrcen Nil 0. 026 0. 004 0. 003 0. 004 Moroaptau Sulfur, Wt. percent. 0. 0001 .0005 0. 0003 Nil Nil Smoke Point 40. 0 39. 0 34. 7 31. 4 30.0 Freezing Point, F 56 -65 06 76 -76 As has been mentioned hereinbefore, gas oils other than the light and medium straight-run gas oils can be used to produce jet fuels contemplated herein. Most feasibly, however, the cracking is carried out in a cycle or in a multiple-pass operation. The following examples illus trate the types of jet fuels that can be thus produced.

EXAMPLES 8 AND 8a The charge stock used in this run was a medium gas oil distilled from a Kuwait crude. This gas oil had the following properties:

A.P.I. gravity 33.8

ASTM distillation:

1.13.1. F 418 50% F 590 E.B.P F 742 Sulfur, weight percent 1.51

A portion of this gas oil was cracked in two stages in the presence of Catalyst A described in Example 1. In the first stage operation, the temperature used was730 F., the hydrogen to oil molar ratio was 40, the liquid hourly space velocity was 0:5, and the pressure was 1000 pounds per square inch gauge. From this operation there was obtained 43.7 volume percent of a product boiling at temperatures higher than about 390 F. This was separated and contacted with the platinum catalyst ina second stage cracking operation.

In the second stage operation, the catalyst temperature employed was 675 F., the hydrogen to oil molar ratio was 40, the liquid hourly space velocity was 0.5, and the pressure was 1000 pounds per square inch gauge. A light jet fuel and a heavy jet fuel were distilled from portions of the effluent product of this operation. Pertinent properties of these jet fuels are set forth in Table III;

9 EXAMPLE 9 The charge stock in this run was a light gas oil obtained by coking a Mid-continent residuum. This coker gas oil had the following properties:

A.P.I. gravity 33.3 ASTM d' tillation:

I.B.P. F 420 50% F.. 535 E.B.P. F 664 Sulfur, weight percent 0.48

This gas oil was subjected to cracking in the presence of the platinum Catalyst A described in Example 1 and of hydrogen in a two-step operation. The temperature employed in the first stage was 770 F., the hydrogen to oil molar ratio was 40, the liquid hourly space velocity was 0.5, and the pressure was 1000 pounds per square inch gauge. Under these conditions, there was obtained 56.8 volume percent of a product boiling at temperatures higher than about 390 F. This material was separated and subjected to cracking in a second stage operation using the platinum Catalyst A described in Example 1.

In the second stage operation, the temperature used was about 700 F. The hydrogen to oil molar ratio was 40, the liquid hourly space velocity was 0.5, and the pressure was 1000 pounds per square inch gauge. Under these conditions, there was produced 48.4 volume percent of a heavy fuel having the properties set forth in Table III.

EXAMPLE 10 The charge stock used in this run was a blend containing one volume of a heavy Kuwait gas oil and five volumes of a cycle stock obtained by cracking Kuwait gas oil in the presence of hydrogen and the platinum Catalyst A, at 730 F., at a pressure of 1000 pounds per square inch gauge, using a hydrogen to hydrocarbon molar ratio of 40 and a liquid hourly space velocity of 0.5. This blend had the following properties:

A.P.I. gravity 40.9 Distillation, vacuum assay:

F 446 50% F 514 95% F 722 Sulfur, weight percent 0.43

The mixture of Kuwait gas oil and cycle stock was cracked in the presence of hydrogen and of the platinum Catalyst A described in Example 1. The temperature employed was 718 F., the hydrogen to oil molar ratio was 40, the liquid hourly space velocity was 0.5 and the pressure was 1000 pounds per square inch gauge. Under these conditions, there was produced 47.9 volume percent of a heavy jet fuel. This jet fuel had the properties set forth in Table III.

EXAMPLES 11 THROUGH 16 For purposes of comparison, a number of straight-run distillate jet fuels were obtained from several crude sources. These jet fuels are typical of those of the prior art. Their properties are set forth in Table IV.

TABLE IV Example 11 12 13 14 15 10 Crude Source East Texas West Kuwait .Taek- Texas son A.P.I. Gravity 41. 0 39. 0 39. 8 40. 0 51. 9 36.3 ASTlVI Distillation:

I.B.P., "F 365 397 374 432 208 280 50% Point, F 438 450 434 487 339 434 E.B.P., F 538 530 554 557 536 526 AnilineGravity Product--- 5, 890 5, 780 5, 215 6, 210 7, 183 4, 740 Total Sulfur, Wt. percent- 0.023 0.05 0. 74 0.82 0.22 0.069 Mercaptan Sulfur, Wt. percent 0.0003 0. 0001 0.0426 0.'000l 0.0038 0.008 Smoke Point 20. 3 23. 0 21. 2'4. 0 19.9 Freezing Point, F 36 30 34 -12 -65 -72 In the evaluation of jet fuels, it has been found that the 50 percent-boiling point of a fuel is determinative of their properties. Thus, for example, if one jet fuel has an initial boiling point of about 300 F., a 50 percentpoint of 400 F. and an end-boiling point of 500 F., and if another jet fuel has a boiling point of 250 F., a 50 percent-point of 400 F. and an end-boiling point of about 550 F, i.e., the same 50 percent-point but different boiling ranges, both fuels will have substantially the same properties with respect to freezing point, Aniline Gravity Product, etc. A comparison of the properties of jet fuels, therefore, can be made on the basis of the mid-boiling point, without taking into consideration the particular boiling range of the fuel.

FIGS. 3 through 8 are based upon the data set forth in Tables I through IV. FIG. 3 shows the relationship between the mid-boiling point and the Aniline Gravity Product of a number of jet fuels of this invention and of typical jet fuels of the prior art. It will be noted that, with one exception, all the jet fuels of the prior art have Aniline Gravity Products substantially lower than 6500. (The exception, Example 15, Table IV, however, has an excessively high sulfur content.) The jet fuels of this invention, on the other hand, all have Aniline Gravity Products higher than 7000. Accordingly, one characteristic that distinguishes the jet fuels of the present invention from those of the prior art is an Aniline Gravity roduct of at least 7000.

FIG. 4 shows the relationship between the mid-boiling point and the total sulfur content of jet fuels of this invention and those of the prior art. It will be noted that, as compared to substantially high sulfur contents in typical jet fuels of the prior art, all the jet fuels of the present invention have sulfur contents lower than 0.04 weight percent. Indeed, the highest sulfur content is 0.026 weight percent. Accordingly, another property of the jet fuels of this invention is a sulfur content of less than 0.04 weight percent.

FIG. 5 shows the relationship between the mid-boiling point and the mercaptan sulfur content of jet fuels of this invention and those of the prior art. It will be noted that all the jet fuels of the present invention have mercaptan sulfur contents lower than 0.0005 weight percent, which is substantially lower than the mercaptan sulfur content of the typical prior art jet fuels. As has been mentioned hereinbefore, it is important for purposes of stability that a jet fuel have a low mercaptan sulfur content. Therefore, another important characteristic of the jet fuels of this invention is a mercaptan sulfur content of less than 0.0005 weight percent.

Another important characteristic of a jet fuel is that it should have a high Smoke Point'so that the combustion chambers and the turbine flange will not be readily fouled by carbon deposits. FIG. 6 shows the relationship between the mid-boiling point and the Smoke Point of the jet fuels of this invention and typical fuels of the prior art. It is to be noted that all the fuels of the present invention have a Smoke Point higher than 30, whereas those of the prior art are substantially lower.

Accordingly, another important characteristic of the jet fuels of this invention is 21 Smoke Point of at least 30.

In FIG. 7, Curve 1 shows the relationship between the mid-boiling point and the A.P.I. Gravity of a jet fuel of the present invention that was made by cracking a Kuwait gas oil. Curve 2 shows the same relationship for a jet fuel of the prior art that was obtained from the same crude source. In the case of the jet fuel of the prior art, it will be noted that there is a substantial increase in the A.P.I. Gravity as the mid-boiling point is lowered. In order to obtain a jet fuel of a given A.P.I. Gravity, therefore, the range of cuts that can be taken is restricted. On the other hand, the A.P.I. Gravity of the jet fuel of the present invention does not vary more than about 2 per 100 F. change in mid-boiling point. This means that the A.P.I. Gravity of the jet fuel of this invention remains substantially constant regardless of the boiling range. Accordingly, the end-boiling point of the IP-S type jet fuel can be higher than is presently specified, i.e. up to about 600 F. and even more. This, of course, permits greater flexibility in selecting a jet fuel for specific requirements. In general, the maximum variation of the A.P.I. Gravity of the jet fuels of this invention per 100 F. change in midboiling is 4 degrees.

FIG. 8 sets forth the relationship between the midboiling point and the freezing point of the jet fuels of the present invention and of typical fuels of the prior art. In all instances, it will be noted that the jet fuels of the present invention have freezing points that are substantially lower than those of the prior art and that the freezing points decrease as the mid-boiling point decreases. The line A-B is FIG. 8 defines a maximum freezing point-50 percent-point relationship of the jet fuels of the present invention. Most jet fuels of the prior art have freezing points that fall above the line A-B. Accordingly, the maximum freezing point of the jet fuels of the present invention, correlated with their mid-boiling points, can be expressed in terms of the formula for the line A-B, namely:

Maximum Freezing Point=0.423

(Mid-boiling Point in F.)226.

In practice, the selection of a maximum freezing point of a jet fuel will be determined largely by the particular operational requirements. Thus, for example, if a fuel is to be used for aircraft operation in the stratosphere or in Arctic climates, it may be desirable to have freezing points of --50 F. or lower. On the other hand, in more temperate climates, higher freezing points may be permissible. It will be noted, however, that regardless of the mid-boiling point, all the jet fuels of the present invention have the following characteristics:

Aniline gravity product min 7000 Total sulfur, wt. percent max 0.04 Mercaptan sulfur, wt. percent max 0. 0005 Smoke point min 30 Variation A.P.I. gravity/ 100 F. change in midboiling point max 4 It is possible, therefore, to produce a jet fuel having any desired boiling range, within the jet fuel boiling range, that will possess all the desirable characteristics described hereinbefore. This permits greater flexibility in. the selection of a jet fuel. Thus, if a very light, volatile fuel is desired, in order to provide for fast starting in operational jet airplanes, it can be obtained and still have all the aforedescribed desirable properties. On the other hand, if the freezingpoint of the jet fuel is a very important consideration, then jet fuel having a mid-boiling point that provides a maximum freezing point in accordance with the line A-B in FIG. 8' can be selected. It will be appreciated, therefore, that the present invention provides a novel class of jet fuels that possess a variety of desirable properties that are not found in the jet fuels of the prior art.

It is recognized that some of the jet fuels of the prior art may have one or more of the desirable characteristics of the fuels of the present invention. Thus, for example, they may have low freezing points or a low sulfur content. It must be appreciated, however, that none of the conventional jet fuels has all the desirable characteristics of the jet fuels of the present invention. Thus, as can be noted from FIG. 6, none of them has a Smoke Point greater than 30. 7

As stated hereinbefore, in the operation of supersonic jet aircraft, the jet combustion fuel is subjected to indirect heat exchange with the jet engine for cooling purposes. This has required the use of additives to stabilize the fuel against the formation of gum and sediment. The jet fuels of the prior art have been difficult to stabilize. On the other hand, the fuels of this invention have good initial stability. Indeed, some of these fuels are extremely stable in the absence of addition agents. Those that may require additives, however, can be stabilized perfectly against the formation of gum and sediment by the use of moderate amounts of suitable additives. A suitable combination of an inhibitor with the jet fuels of this invention, is described hereinafter.

The heat stability of the jet fuels is determined by the Erdco Coker Test developed by Pratt & Whitney Aircraft. In this test, the test fuel is pumped over an electricallyheated tube and thence through a heated, sintered stainless steel filter. The test fuel is pumped at a flow rate of 4 pounds per hour. The fuel exit temperature from the heat exchange section (the electrically-heated tube) is 400 F., the filter temperature is 500 F, and the fuel pressure is 15 0 p.s.i.g. The fuel stability is rated by measuring the pressure drop across the filter and operating the test until the pressure drop across the filter (because of build-up of sediment and gum) is equivalent to 25 inches of mercury. The time is noted when a pressure drop equivalent to l, 5, 1O, 15, 20, and 25 inches of mercury is obtained. An acceptable fuel should show a pressure drop equivalent to less than 25 inches of mercury across the filter after 300 minutes. The test is preferably run for 600 minutes or until the 25-inch pressure drop is obtained, whichever occurs first. This test simulates conditions in a jet engine. It will be appreciated that, from the standpoint of time, the longer a fuel lasts in the test, the longer will be the period of operation of a jet engine before it must be cleaned.

EXAMPLE 17 A jet fuel was produced by cracking alight Kuwait gas oil in the presence of hydrogen and of a platinum catalyst, in a once-through operation, as described hereinbefo-re. This gas oil was cracked at 690 F., at a liquid hourly space velocity of 0.45, at a pressure of about 1000 pounds per square inch gauge, and using a hydrogen to hydrocarbon molar ratio of 43. Thi fuel had an A.P.I. Gravity of 46.8", an initial boiling point of 338 F., a 50 percentpoint of 434 F., and an end-boiling point of 501 F. This fuel, uninhibited, was subjected to the Erdco Coker Test, and showed no pressure drop after 600 minutes.

As mentioned hereinbefore, some jet fuels of this invention are sufficiently stable that no additives are required. This is illustrated by Example 17. It will be noted that this fuel, obtained by cracking a Kuwait gas oil, had complete stability even after 600 minutes on test.

In cases in which it is desirable to stabilize the jet fuels of the present invention, it can be done by the addition of amines. In general, these materials are primary alkylamines that have a tertiary carbon atom attached to the nitrogen atom and one or more recurring tertiary butyl groups and which contain between 8 and 24 carbon atoms per .alkyl radical. Thus, the octyl'amine has the structure:

CH3 H CH CH3 H CH3 The other amines have a similar structure. Non-limiting examples are l,l,3,3-tetramethyl octylamine; 1,1-dimethyl octadecylamine; and l,l,3,3 tetramethyl decylarnine. It is contemplated to use mixtures of these amines, as well as relatively pure amines. The amine additive is added to the fuel in concentrations varying between about Y10 and about 200 pounds per thousand barrels of fuel, preferably, between about 10 and about 100' pound per thousand barrels of fuel. In terms of weight percent, based upon the weight of the fuel, the concentrations vary, preferably, between about 0.005 percent and about 0.05 percent.

If desired, the jet fuels of this invention can contain other additives for the purpose of improving or imparting other properties. Thus, for example, antioxidants, such as 2,4-di-ter-tiarybutyl-6-methylphenol, N,N'-di-secondary butyl-paraphenylenediamine, and 2,4-dimethyl-6-tertiarybutyl-phenol; metal deactivators, such as N,N'-disalicylidene-LZ-propanediarnine; antitrust agents, such as dimeric fatty acids and raryl sulfonates; and burning and igition quality improvers, such as dinitropropane and amyl ni trate, can be added in amounts sufiicient to improve or impart to the fuels oxidation stability, antirust characteristics, superior burning performance, etc.

Although the present invention has been described with preferred embodiments, it is to be understood that modifications and variations may be resorted to, without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such variations and modifications are considered to be Within the purview and scope of the appended claims.

What is claimed is:

1. A jet combustion fuel consisting essentially of a hydrocracked distillate hydrocarbon fraction prepared by hydrocracking a hydrocarbon fraction with an initial boiling point of at least about 400 F. and an end boiling point of at least about 600 F. in the presence of hydrogen over a catalyst containing 0.1 to weight percent of at least one metal selected from the group consisting of metals having atomic numbers of 44 to 46, inclusive, and 76 to 78, inclusive, deposited upon a solid refractory support having an Activity Index of at least about 25 at a temperature between about 500 F. and about 825 F., a hydrogen pressure of about 500 p.s.i.g. to about 2500 p.s.i.g. and a hydrogen-to-hydrocarbon mole ratio of about 2 to about 80 such that the cracking level is at least about 20 volume percent per pass, and separating from the hydrocracked product a jet combustion fuel having an initial boiling point falling within the range varying between about 200 F. and about 400 F., a 50 percentpoint of at least about 325 F., and an end boiling point falling within the range varying between about 450 F. and about 600 F., and which boils substantially continuously between said initial boiling point and said end boiling point over a boiling range extending at least 75 degrees on the Fahrenheit scale; and which has all the following characteristics:

(a) an Aniline-Gravity Product of at least about 7000;

(b) a total sulfur content of less than about 0.04 percent, by weight;

(c) a mercaptan sulfur content of less than about 0.0005 percent, by weight;

(d) a Smoke Point of at least about 30;

(e) a rate of charge in A.P.I. Gravity of less than about 4 per 100 F. change in the 50 percent-point;

(f) a freezing point that is lower than the value determined by the formula: 0.423 (Mid-boiling Point in F.)226; and

(g) a her-rnal stability such that when uninhibited it will pass a test therefore equivalent to the Erdco Coker Test with a pressure drop equivalent to less than 25 inches of mercury across the filter after 300 minutes.

2. A jet combustion fuel consisting essentially of a hydrocracked distillate hydrocarbon fraction prepared by hydrocracking a hydrocarbon fraction with an initial boiling point of at least about 400 F. and an end boiling point of at least about 600 F. in the presence of hydrogen over a catalyst containing 0.1 to 5 Weight percent of at least one metal selected from the group consisting of metals having atomic numbers of 44 to 46, inclusive, and 76 to 78, inclusive, deposited upon a solid refractory support having an Activity Index of at least about 25 at a temperature between about 500 F. and about 825 F., a hydrogen pressure of about 500 p.s.i.g. to about 2500 p.s.i.g. and a hydrogen-to-hydrocarbon mole ratio of about 2 to about 80 such that the cracking level is at least about 20 volume percent per pass, and separating from the hydrocracked product a jet combustion fuel having an initial boiling point falling within the range varying between about 200 F. and about 275 F., a 50 percent-point of at least about 325 F., and an end boiling point falling within the range varying between about 450 F. and about 550 F., and which boils substantially continuously between said initial boiling point and said end boiling point over a boiling range extending at least degrees on the Fahrenheit scale; and which has all the following characteristics:

(a) an Aniline-Gravity Product of at least about 7000;

(b) a total sulfur content of less than about 0.04 percent, by weight;

(c) a mercaptan sulfur content of less than about 0.0005 percent, by weight;

(:1) a Smoke Point of at least about 30;

(e) a rate of change in A.P.I. Gravity of less than about 4 per 100 F. change in the 50 percent-point; (f) a freezing point that is lower than the value determined by the formula: 0.423 (Mid-boiling Point in F)226; and

(g) a thermal stability such that when uninhibited it will pass a test therefore equivalent to the Erdco Coker Test with a pressure drop equivalent to less than 25 inches of mercury across the filter after 300 minutes.

3. A jet combustion fuel consisting essentially of a hydrocracked distillate hydrocarbon fraction prepared by hydrocracking a hydrocarbon fraction with an initial boiling point of at least about 400 F. and an end boiling point of at least about 600 F. in the presence of hydrogen over a catalyst containing 0.1 to 5 weight percent of at least one metal selected from the group consisting of metals having atomic numbers of 44 to 46, inclusive, and 76 to 78, inclusive, deposited upon a solid refractory support having an Activity Index of at least about 25 at a temperature between about 500 F. and about 825 F., a hydrogen pressure of about 500 p.s.i.g. to about 2500 p.s.i.g. and a hydrogen-to-hydrocarbon mole ratio of about 2 to about 80 such that the cracking level is at least about 20 volume percent per pass, and separating from the hydrocracked product a jet combustion fuel having an initial boiling point falling within the range varying between about 275 F. and about 400 F., a 50 percent-point of at least about 325 F., and an end boiling point falling within the range varying between about 500 F. and about 600 F., and which boils substantially continuously between said initial boiling point and said end boiling point over a boiling range extending at least 75 degrees on the Fahrenheit scale; and which has all the following characteristics:

(11) an Aniline-Gravity Product of at least about 7000; (b) a total sulfur content of less than about 0.04 percent, by weight;

(c) a mercaptan sulfur content of less than about 0.0005 percent, by weight;

(d) a Smoke Point of at least about 30;

(e) a rate of change in A.P.I. Gravity of less than about 4 per F. change in the 50 percent-point;

(f) a freezing point that is lower than the value determined by the formula: 0.423 (Mid-boiling Point in F )226; and

15 16 (g) a thermal stability such that when uninhibited it References Cited in the file of this patent Wm Pass a test therefore equivalent to the Erdco Guthrie: Petroleum Processing, October 1952, pp. Coker Test with a pressure drop equivalent to less 14254429 than 25 inches of mercury across the filter after 300 Kelley; The Petroleum Engineer, November 1952, minutes. 5' pp. C7 to Cl0.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3 150 071 September 22 1964 Frank G Ciapetta et all.

It is hereby certified that error appears in the above numbered patent reg-firing correction and that the said Letters Patentshould read as corrected below. 7

Column 2 line 34, for "lower" read lowest column 5, line 48, for "oils between" read oils boil between column 7 line 75 for "as" read was column ll line 32 for "is" read in column l3 line "2O for "igition" read ignition Signed and sealed this 12th day of January 1965 (SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents ERNEST W; S-WIDER Aitesting Officer 

1. A JET COMBUSTION FUEL CONSISTING ESSENTIALLY OF A HYDROCRACKED DISTILLATE HYDROCARBON FRACTION PREPARED BY HYDROCRACKING A HYDROCARBON FRACTION WITH AN INITIAL BOILING POINT OF AT LEAST ABOUT 400*F. AND AN END BOILING POINT OF AT LEAST ABOUT 600*F. IN THE PRESENCE OF HYDROGEN OVER A CATALYST CONTAINING 0.1 TO 5 PERCENT OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF METALS HAVING ATOMIC NUMBERS OF 44 TO 46, INCLUSIVE, AND 76 TO 78, INCLUSIVE, DEPOSITED UPON A SOLID REFRACTORY SUPPORT HAVING AN ACTIVITY INDEX OF AT LEAST ABOUT 25 AT A TEMPERATURE BETWEEN ABOUT 500*F. AND ABOUT 825*F., A HYDROGEN PRESSURE OF ABOUT 500 P.S.I.G. TO ABOUT 2500 P.S.I.G. AND A HYDROGEN-TO HYDROCARBON MOLE RATIO OF ABOUT 2 TO ABOUT 80 SUCH THAT THE CRACKING LEVEL IS AT LEAST ABOUT 20 VOLUME PERCENT PER PASS, AND SEPARATING FROM THE HYDROCRACKED PRODUCT A JET COMBUSTION FUEL HAVING AN INTIAL BOILING POINT FALLING WITHIN THE RANGE VARYING BETWEEN ABOUT 200*F. AND ABOUT 400*F., A 50 PERCENTPOINT OF AT LEAST ABOUT 325*F., AND AN END BOILING POINT FALLING WITHIN THE RANGE VARYING BETWEEN ABOUT 450*F. AND ABOUT 600*F., AND WHICH BOILS SUBSTANTIALLY CONTINUOUSLY BETWEEN SAID INITIAL BOILING AND SAID END BOILING POINT OVER A BOILING RANGE-EXTENDING AT LEAST 75 DEGREES ON THE FAHRENHEIT SCALE; AND WHICH HAS ALL THE FOLLOWING CHARACTERISTICS: (A) AN ANILINE-GRAVITY PRODUCT OF AT LEAST ABOUT 7000; (B) A TOTAL SULFUR CONTENT OF LESS THAN ABOUT 0.04 PERCENT, BY WEIGHT; (C) A MERCAPTAN SULFUR CONTENT OF LESS THAN ABOUT 0.0005 PERCENT, BY WEIGHT; (D) A SMOKE POINT OF AT LEAST ABOUT 30; (E) A RATE OF CHARGE IN A.P.I. GRAVITY OF LESS THAN ABOUT 4* PER 100*F. CHANGE IN THE 50 PERCENT-POINT; (F) A FREEZING POINT THAT IS LOWER THAN THE VALUE DETERMINED BY THE FORMULA: 0.423 (MID-BOILING POINT IN *F.)-226; AND (G) A HERMAL STABILITY SUCH THAT WHEN UNINHIBITED IT WILL PASS A TEST THEREFORE EQUIVALENT TO THE ERDCO COKER TEST WITH A PRESSURE DROP EQUIVALENT TO LESS THAN 25 INCHES OF MERCURY ACROSS THE FILTER AFTER 300 MINUTES. 